On Wed, Sep 06, 2017 at 04:00:56PM +0200, Javier González wrote: > > Nope. You want to loop over vmalloc_to_page and call bio_add_page > > for each page, > > Yes. This is basically what I did before. > > > after taking care of virtually tagged caches instead > > of this bounce buffering. > > And thus I considered bio_copy_kern to be a better solution, since it > will through time take care of doing the vmalloc_to_page correctly for > all cases. bio_copy_kern copies all the data, so it is generally not a good idea. The cache flushing isn't too hard - take a look at the XFS buffer cache for an existing version. It would be good to just to do the right thing inside bio_map_kern for that so that callers don't need to care if it is vmalloced or not. > Ok. So this would mean that targets (e.g., pblk) deal with struct > request instead of only dealing with bios and then letting the LightNVM > core transforming bios to requests. This way we can directly map to the > request. Is this what you mean? Yes. > Just out of curiosity, why is forming the bio trough bio_copy_kern (or > manually doing the same) and then transforming to a request incorrect / > worse? Because you expose yourself to the details of mapping a bio to request. We had to export blk_init_request_from_bio just for lightnvm to do this, and it also has to do weird other bits about requests. If you go through blk_rq_map_* the block layer takes care of all that for you.
